This project will involve a continuation of the study of the basic mechanism of action of pneumococcal cytolysin. This will include the role of the erythrocyte in the lytic process and the determination of the number of sites on the toxin molecule which interact with the erythrocyte membrane. Studies on the mechanism of corneal damage by microbial toxins will also continue and will involve cytolysins from Streptococcus pneumoniae, Staphylococcus aureus and pseudomonas aeruginosa. Effects of toxins on enzyme release from isolated leucocytes and lysin-treated corneas will be included.